Boxtech Shrimp Feeding Dish Set, Aquarium Fish Feeder Tube Kit with Feeding Ring,Cleaning Brush for Fish Tank

How high can this be used in aquariums?

Can this be used in salt water tanks?

Does this work for dwarf African frogs?

Can someone please post a picture of the ring up close? Is the ring just the ring or is there something that keeps the food floating while in the tank